Muffler



July 14, 1936 G. c. sTARKwL-:ATHER ET Al. 2,047,442

July 14, 1936 G. c. STARKWEATHER ET A1. 2,047,442

MUFFLER Filed Aug. l5, 1955 j 2 Sheets-Sheet 2 Patented July 14, 1936UNITED STATES PATENT VFFICE Haas, Buffalo, N. Y.,

assignors to Buffalo Pressed Steel Company, Buialo, N. Y.

Application August 15, 1935, Serial No. 36,352

16 Claims. (Cl. 181-48) 'Ihis invention relates to improvements inmufflers or silencers, such for example as are used in connection withthe silencing of noises of the exhaust or intake of internal combustionengines.

The objects of this invention are to provide a muilier of this kind ofimproved and simplified construction and having greatly increasedsilencing properties; also to provide a muffler of this kind providedwith an inner conduit through which gases and sound waves may passdirectly from one end of the conduit to the other, and which is providedwith a relatively slight restriction and with perforations or aperturesarranged forwardly and rearwardly of the restrictions, so that a greaterproportion of the sound waves will pass out of and again into the innerconduit through the perforations than would pass through perforations ofa similar conduit without such restrictions; also to provide a muier ofthis kind in which the inner conduit is arranged within a shell and' inwhich means are provided for deflecting sound waves approximatelytangentially of the inner shell into the space between the two shells.

A further object of the invention is to provide a muffler or silencerwhich will be effective in reducing the sounds accompanying the flow ofgas through the same, and which will have a very low resistance to theow of gas through the same, which will aid in the rapid dissipation ofheat from the exhaust gases and which will be light in weight and strongstructurally.

Another object of the invention is to provide an improved and simplifiedconstruction for forming an intermediate shell for a muffler.

Further objects of the invention are to improve the construction ofmuiiiers in other respects hereinafter specified.

The muier shown in the accompanying drawings is designed primarily foruse in connection with the silencing of the exhaust of internalcombustion engines, but it will be understood that the muiiier may beused for other purposes, such, for example, as the silencing oftheintake to the engine.

In the accompanying drawings:

Fig. l is a longitudinal central sectional view of a mufiier embodyingthis invention.

Fig. 2 is a similar view of a muffler of modified construction. i

Fig. 3 is a similar view of a muier of still another construction.

Fig. 4 is a transverse sectional view, on line 4 4, Fig. 2.

Fig. 5 is a fragmentary longitudinal sectional view of a portion of aninner conduit of a muffler of modified construction.

In all of theconstructions shown, A represents the outer shell of themufller and one end of each mufer is provided with a head B secured 5-to the outer shell A and having a tubular extenn sion or intake duct b,which may, for example, be formed integrally with the head B and withwhich an exhaust pipe D leading from an engine may be connected. Eachmuilier also has a disl0 charge head C and a duct c connected therewithto which a tail pipe may be secured. The outer shell and the heads ofthe muiiler may be of any suitable or desired construction and ofthemselves do not constitute a part of this invention.

In all of the muiilers shown, the inner conduit or shell is of theuninterrupted or through type and is provided with perforationsthroughout a large part of its length so that gases and sound waves maypass through the inner conduit from one end thereof to the other, andcertain portions. of the gases and sound waves may pass into and out ofthe inner conduit through the perforations or apertures in the conduit.The conduit is preferably of a slightly smaller diameter'25 than theexhaust pipe-and the diameter of this conduit should not materiallyexceedthat of the tail or discharge pipe.

The inner conduits in most muiilers of this type have heretofore beenmade of uniform diameter 3U throughout or of tapering form and generallymuffiers of this kind have been provided with resonance chambersarranged between the outer shell and the conduit for reducing the noisesof the exhaust gases. In accordance with this invention, the silencingeffect of muiiiers is greatly reduced by providing the inner conduit atintervals with restrictions or contractions, which effect a reduction inthe cross sectional area of the inner conduit at one or more placeslength- 40 wise of the conduit. These restrictions while very slightlyincreasing the back pressure of the muliier, have the property ofcausing a much greater percentage of the gases and sound waves to iiowoutwardly through the perforations in the inner conduit, and then backagain through other perforations into this conduit and this action inturn greatly increases the silencing effeet of the muiiier with apractically negligible amount in increase in back pressure. Possibly theincreased silencing effect is due to the fact that sound waves passingout of the inner conduit through perforations in the same and then backagain into the inner conduit will, because of the increased distancethrough which they have traveled, upon returning into the conduit be outof phase with sound waves that have passed straight through therestriction in the conduit. The silencing effect may be furtherincreased by providing the inner conduit with suitable means, such aslouvres for causing the gases, and possibly sound waves, which pass outthrough the perforations in the inner conduit, to be deected in anapproximately tangential direction. These louvres may be arranged tocause a whirling or rotary movement of gases in the space or spacessurrounding the inner conduit. This causes sound waves to travel aroundthe inner conduit in a somewhat helical path, and consequently, thedistance through which such sound waves must travel is furtherincreased, thus ythrowing the sound waves returning into the conduitfurther out of phase with those sound waves which have passed straightthrough the conduit.

One or more restrictions or contractions of the inner conduit mayeffectively be used in connection with various types of resonating orsound absorbing chambers arranged in the space be tween the innerconduit and the outer shell ci the muliler, and one or more intermediateshells together with baiiles may be employed in connection with theserestrictions in the inner conduit. It has been found, however, that whenan inner conduit is provided with restrictions or contractions of thistype and arranged with referu ence to the perorations in the innerconduit as herein described, the number of resonance or sound deadeningchambers in themuiiier may be greatly reduced without sacriiicingsilencing efiect and the cost and weight of the muiiier is,consequently, proportionately reduced.

In order to illustrate this invention, certain simplified forms ofinuiilers embodying the invention are illustrated in the drawings, butit will be understood that this invention is usable in connection withmuriers of many other types.

In Fig. l, l@ represents the inner conduit of the muiiler which isprovided with a relatively large number of small periorations lldistributed throughout the greater part of the length oi the innerconduit. The inner conduit in this construction is connected at its endswith the heads b and c, and the conduit receives gases and sound wavesat one end thereof,for exampleirom the inlet duct c and discharges thegasthroug'h discharge duct b. rThe perforations or apertures lll in theinner conduit are preferably associated with louvers or deflectors,which may, for example, be formed integrally with the conduit it, andwhich are so arranged that gases which pass outwardly through theseperforations or apertures into the space between the conduit and outershell, will be deflected tangentially oi the conduit. The louvers m'ayall face in the same direction tangentially or may be arranged to opposeeach other, or alternate groups of louvers lengthwise of the conduit mayface in opposite directions to produce diierent bodies of gaseslengthwise of the muilier which move in opposite directions. Fig. 4shows an arrangement whereby the louvers on one half of the conduit facein a direction opposite to the louvers on the other half.

The inner conduit lll shown in Fig. l, is provided at intervals withunperforated portions, and suitable restrictions, such for example, asbaies or restricting members i 5, may be secured within the innerconduit, three such restricting members being illustrated in Fig. l.Each restricting member as shown has a substantially cylindrical portionI 6 iitting within the inner diameter of the conduit l and securedthereto, for example, by welding. The sm'allest inner diameter of therestricting member is large enough to provide for an ample ow of gasesand sound waves through the restricting member, but at the same time toretard the flow sufficiently to cause a considerable portion of the gasand sound waves to pass outwardly through the apertures or perforationsll arranged ahead of the restrictions l5. For example, the muiilers inwhich the inner conduit is of 1.75 inches internal diameter, thesmallest internal diameter of the restricting members may be from ll/rto lll/2 inches, this diameter varying in accordance with the amount ofsilencing eect that must be produced. i

It is also a desirable feature of this invention that the passage ofgases through the apertures or perorations il be facilitated as much aspossible and for this purpose, it is preferred that the combined areasof the openings in the inner conduit in advance or ahead of arestriction be not less than the cross sectional area of the restrictingmember measured at its smallest internal diameter. Similarly theapertures rearwardly of a restriction, through which gases and soundwaves may re-enter the conduit, should have a combined area of at leastthat of the smallest internal diameter of the restriction.

It will be noted in Fig. 1 that no sound absorbing or deiiecting devicesare provided in the space betweenthe conduit and the outer shell A. Amuffler or" this kind, nevertheless, produces very eiectlve silencingand this may be due to the fact that sound waves passing out through theapertures ahead of the nrst restricting member l5 may pass through thespace between the conduit and outer Shell either to the aperturesimmediately in rear of the rst restricting member l5, or to thoseapertures in rear of the second or the third restricting members.Because of the tangential deflection of gases and sound Waves by thelouvers and because of the movement of the gases in the space betweenthe outer shell and the central conduit, sound waves entering thediierent sets of apertures will be out of phase to diierent degrees withrespect to those sound waves which have passed straight through theinner conduit, and consequently, a very eiective silencing will result,it being understood, of course, that if two equal sound waves arebrought together which are completely out of phase with one another, sothat the crest of one wave coincides with the trough of the other wave,the sound will be eliminated.

In Fig. 2, a muler lis shown in which the inner perforate conduit 2lihaving apertures 2l is connected with the end heads of the muiersubstantially in the same manner as the mufer shown in Fig. 1. In thisconstruction, however, only two restrictions 22 are provided within theinner conduit, which are of a construction similar to that shown in Fig.l. In this construction, the space between the inner conduit and theouter shell is shown as divided by means of a transverse batie 24 intotwo spaces. It will be noted too that the baiile 2&3 is located in aplane intermediate between the two restricting members 22. For certainengines, a muiler having a transverse barile in the outer shell has beenfound desirable, since this'produces between the bailie 24 and the headB of the muffler a chamber in which the sound waves and gas arecontrolled, so that they will pass back into the inner conduit throughthe apertures or perforations spaced between'the first restrictingmember 22 and the baille 24. If desired, a number of baiiles similar tothe baille 24 may be provided at intervals lengthwise of the muiiier, insimilar spaced relation to the restrictions in the inner conduit, andthe baille may be perforated or unperforated as desired.

The muilier shown in Fig. 2 is also provided at the opposite end thereofwith a short intermediate shell 25 extending about the two groups ofapertures in the inner shell or conduit. This intermediate shell formswith the inner shell small resonating chambers 29 and 30 communieating.with the interior of the conduit through the apertures. These resonatingchambers have been found particularly desirable in connection with thesuppressing of high frequency sound waves. While only two of these highfrequency resonating chambers 29 and 3U are provided, it will be obviousthat the number of these chambers may be increased or decreased,depending upon the extent to which such chambers are found necessary forsilencing a particular en- The intermediate shell 25 also forms with theouter shell A an imperforate resonator space 3l, into which sound wavesforced out ofthe inner conduit by means of the second restriction shownin Fig. 2 may enter. Some ofO these sound waves when travelling to theend of the space and being deflected back bythe head C, are then out ofphase with other sound waves passing through the inner conduit. 'lhisportion of the muler operates in conjunction with longer and lowerfrequency sound waves, so thati by means ofthe arrangement of theintermediate shell, as shown, two types of sound waves are eliminated.It will, of course, be understood that.the intermediate shell 25 may beused'in a muilier of this type l without the baille 24, and the bame 24may also be used without the intermediate shell 25 but preferably, if,another transverse baille is used between the conduit and outer shell,an additional restriction is provided in the conduit. Such construction,for example, is shown in Fig. 3, in which two transverse baiiies 34 areemployed and three restrictingv members 35. It will be noted in Fig. 3that each restriction is spaced between two groups of apertures, onegroup being located in advance of the restricting member and the otherrearwardly thereof in the direction of flow of the gases through theinner conduit. When baflles are employed between the inner conduit andan outer shell, such bailles are preferably arranged so that at leasttwo groups of apertures and a restricting member are located in advanceor ln rear of the baille, so that a bypass around the inner conduit isprovided.

Fig. 4 illustrates louvers 38, such as may be used on any of themuillers shown in Figs. 1 to 3. These louvers are preferably formedintegrally with the inner conduit 31 and each louver projects over itsaperture in such a manner that the gases and sound waves dischargedthrough the apertures will be deflected substantially tangentially withreference to the conduit.

In place of restricting members formed separately and secured within theinner conduit, other means may, of course, be employed to provide thenecessary restriction within this conduit andby way of example analternative construction for producing a restriction within the conduitis illustrated in Fig. 5, in which the inner conduit 40 is provided withan annular portion 4I which extends inwardly and forms a restriction inthe conduit. The restriction 4l may be pressed or rolled inwardly in anysuitable or desired manner.

It has also been found very desirable'to construct the muillers in sucha manner that the inner conduit is of a diameter which is preferably nogreater than, or at least not materially greater than the diameter ofthe exhaust pipe D.

'I'he restrictions in the inner conduit togetherV with the arrangementfor causing a relatively large portion of the gases and sound waves totake a longer path around the^inner conduit vbefore returning to thesame, have been found weight and of lower cost than muillers hereto foreused and having silencing effect equal or superior to those heretoforeproduced. The use of restrictions in the inner conduit as hereindescribed, since it eliminates or reduces the need for some or all ofthe intermediate shells heretofore used, also more readily dissipatesthe heat of the gases discharged into the muiller, since a largeproportion of the gases passing through the muiller contact with theouter shellfwhich in turn is cooled directly by the surroundingatmosphere. 'I'his construction also lends itself particularly well foruse in connection with many kinds of mulllers heretofore devised, sinceit may be easily applied to such muillers to materially increase thesilencing effects of the same. It will, consequently, be understood thatthe particular constructions illustrated and described'are merelyillustrative of a few applications of this invention to mulilers. l

'I'he restrictions in the inner conduit of the mufller have also beenfound to eliminate or materially reduce the swishing or hissing noisesfrequently made by perforate conduits in mumers as heretoforeconstructed. This may possibly be due to the fact that the restrictionstend to cause the gases to pass mainly through the axial portion of theconduit and to reduce the iiow of gases close to the wall of the conduitacross the perforations in the conduit, or to the fact that a greaterflow of gases through the perforations divided lengthwise into aplurality of parts.

As shown, this shell ismade in two halves which may be secured togetherlengthwise of the muler and also secured to another muffler shell. In.this construction, the intermediate shell of the muiller is formed intwo half shells 26 and 21, both of these half shells being provided withlaterally extending iianges 4| which may readily be secured together bywelding or other means. By forming a muiiler shell in thismanner, theuse of bafiies connecting the shell with an adjacent shell may bedispensed with since each half shell may be provided with webs. orportions 42 which terminate in substantially semi-cylindrical portions43 adapted to be secured to an adjacent shell or securely held in placeby other connections, such as the longitudinal anges 4|. The webs orportions 42 may be of any desired depth, so that the space between thecylindrical portion of the two half shells and the adjacent shell towhich they are connected may be varied as may be necessary to obtain thedesired silencing eil'ects. In the form illustrated, the webs 42 extendinwardly to engage with a shell arranged within the longitudinallydivided shell, but obviously they could be formed to extend outwardly toengage with a. shell arranged about the divided shell. The cylindricalportions 43 are preferably welded or secured to unperforated portions ofthe adjacent shell. If desired, however, one or more of the webs 42 maybe omitted, so that chambers of diderent lengths may be formed or achamber that is open at one end, so that. for example, the chamber 29could communicate with the chamber 3l.

, We claim as our invention:

1. A muiiler having an inlet end arranged to connect with an exhaustpipe of an internal combustion engine and having a discharge passage atthe other end thereof, of a conduit in said muftler forming a passagefrom the inlet to the other end of said muiiler, said conduit having anexternal diameter no greater than the external diameter of said exhaustpipe and apertured throughout the greater part of the length thereof, ashell surrounding said conduit, and a' plurality of restrictionsarranged at intervals lengthwise of said conduit to reduce noise made bygases flowing across the perforations in said conduit, the innerdiameter of said restrictionsbeing at least two-thirds of the innerdiameter of adjacent.

portions of said conduit. y

2. A muler having an inlet end arranged to connect with an exhaust pipeof an internal combustion engine and having a discharge passage at theother end thereof, of a conduit in said muiiler forming a passage fromthe inlet to the other end of said muiiier, said conduit having anexternal diameter no greater than the external diameter of said exhaustpipe and apertured throughout the greater part of the length thereof, ashell surrounding said conduit, and a restriction in said conduitarranged with apertures before and behind said restriction, saidrestriction forcing a portion of the gas and sound waves entering saidmufiler to pass out of perforations arranged ahead of said restrictionand to pass about said conduit in the space between said conduit andsaid shell, and then to return to said conduit through perforationslocated behind said restriction, the opening in said restriction beingAat least two-thirds of. that of adjacent portions of said conduit.

3. A muiiler having a conduit open at both ends to receive gases in oneend thereof, and discharge gases from the opposite end thereof andextending continuously from end to end of said muf- `iler, a shellsurrounding said conduit to form a closed chamber about said conduit,said conduit having a restriction intermediate of the ends thereof, andperforations in said conduit both before and behind said restriction topermit sound waves and gases to pass out of perforations before reachingsaid restriction and to pass in said chamber through perforations insaid conduit behind said restriction, the opening in said restrictionbeing at least two-thirds of that of adjacent portions of said conduit.

4. A muilier having an outer shell and a conduit confined within saidshell and forming a..

continuous passage from end to end thereof for the greater portion ofthe gases entering said conduit and having perforations through which alesser portion of the gases and sound waves may pass to and from thespace between said shell and said conduit, and a restriction in saidconduit and so arranged relatively to said perforations that certain ofsaid perforations are lo- 5 cated forwardly, and others rearwardly ofsaid restriction, with reference to the ow of gases through saidconduit, the opening in said restriction being at least two-thirds ofthat of adjacent portions of said conduit.

5. A muiiier having an outer shell and a conduit confined within saidshell and forming a continuous passage from end to end thereof for thegreater portion of the gases entering said conduit and havingperforations through which a lesser portion of the gases and sound wavesmay pass to and from the space between said shell and said conduit,means associated with said perforations' to cause gases dischargedthrough said perforations to move about the axis of said conduit in thespace between said shell and conduit, and a restriction in said conduitand so arranged relatively to said perforations that certain of saidperforations are located forwardly, and others rearwardly of saidrestriction, with reference to the ow of gases through said conduit.

6. A muiiier including an outer shell, an inner conduit arranged withinsaid shell and forming a.w continuous passage for gases through saidmuilier and having perforations throughout the greater part of thelength thereof, a plurality of l restrictions in said conduit spacedfrom each other and each arranged between perforations locatedrearwardly and forwardly of said restriction with reference to thedirection of flow of gases though said conduit, the inner diameter ofsaid restrictions being at least two-thirds of the inner damter ofadjacent portions of said conduit.

7. A muilier including an outer shell, an inner conduit arranged withinsaid shell and forming a continuous passage for gases through saidmuiiier and having perforations throughout the greater part of thelength thereof, a. plurality of restrictions in said conduit spaced fromeach other and each arranged between perforations located rearwardly andforwardly of said restriction with reference to the direction of iiow ofgases through said conduit, the internal diameter of said restrictionbeing at least two-thirds of the diameter of adjacent parts of saidconduit, and means associated with said perforations to direct gases andsound waves discharged through said perforations substantiallytangentially of said conduit.

8. A muffler including an outer shell, an inner conduit arrangediwithinsaid shell and forming 'a continuous passage for gases through saidtween said shell and conduit from perforations 4" forwardly of arestriction to perforations located rearwardly of said restriction.

` 9. A muiller including an cuter shell, f an inner conduit arrangedwithin said shell and forming a continuous passage for gases throughsaid muiiler and having perforations throughout the greater part of thelength thereof, a plurality of restrictions in said conduit spaced fromeach other and each arranged between perforations located rearwardly andforwardly of said restriction with reference to the direction of flow ofgases through said conduit, and a baille connecting said conduit andshell and spaced about said conduit at a portion thereof intermediate ofadjacent restrictions, and restricting the passage of gases and soundwaves through the space between said shell and conduit from perforationsforwardly1 of a restriction to perforations located rearwardly of saidrestriction, the combined areas of the perforations through which gasesmay flow out of or into said conduit about a restriction being at leastequal to the cross sectional area oi the smallest passage through saidrestriction.

10. A muiiier having a straight substantially uninterrupted perforateconduit for gas and sound waves, a shell surrounding said conduit andforming a closed space about said conduit into and out of which gasesand sound waves can pass only through the perforations in said conduit,said conduit having a small restriction therein intermediate of its endsto produce a slight resistance to the iiow of gases through saidconduit, which causes a portion of said gases to bypass around saidrestriction through the space between said conduit and shell and whichpermits a larger portion of gases and sound waves to pass through saidrestriction.

11. A muilier having a straight substantially uninterrupted perforateconduit for' gas and sound waves, a shell surrounding said conduit, andforming a closed space about said conduit into and out of which gasesand sound waves can pass only through the perforations in said conduit,said conduit having a restriction therein intermediate of its ends toproduce a resistance to the ow oi gases through said conduit, whichcauses a portion of said gases to bypass around said restriction throughthe space between said conduit and shell, and which permits a largerportion of gases and sound waves to pass through said restriction, andmeans associated with said perforations for directing gases and soundwaves discharged therethrough in a direction substantially tangentiallyof said conduit.

12. A muffler having a substantially uninterrupted perforate conduit forgas and sound waves, an outer shell surrounding said conduit andforniing a closed space about said conduit into which gases and soundwaves can pass only through the perforations in said conduit, saidconduit having a restriction therein spaced intermediate of its ends andbetween perforations, to cause gases and sound waves to pass throughperiorations ahead of said restriction into the space between saidconduit and said outer shell and then back into said conduit throughperforations located rearwardly of said restriction, and an intermediateshell spaced between a periorate portion of said conduit and said outershell and forming with said conduit sound absorbing chambers ior highfrequency sound waves and spaced from said restriction, saidintermediate shell forming with said outer shell a resonance chamber forlow frequency sound waves, which is closed at one end and communicateswith said conduit at its other and.

13. A muiiler having a substantially uninterrupted perforate conduit forgas and sound waves, an outer shell surrounding said conduit and forminga closed space about said conduit into which gases and sound waves canpass only through the perforations in said conduit, said conduit havinga plurality of restrictions therein spaced apart, each restriction insaid .conduit being spaced between two groups of perforations, one groupbeing located in advance of said restriction and the other group beinglocated rearwardly of said restriction, and a baille connecting the saidconduit and said outer shell and spaced between the two groups ofperforations of one restriction and the two groups of perforations ofanother restriction.-

14. A muler having a substantially uninterrupted perforate conduit forgas and sound waves, an outer shell surrounding said conduit and forminga closed space about said conduit into which gases and sound waves canpass only through the perforations in said conduit, said conduit havinga plurality of restrictions therein spaced apart, each restriction insaid conduit being spaced between two groups of perforations, one groupbeing located in advance of said restriction and the othergroup beinglocated rearwardly of said restriction, and a baffle connecting the saidconduit and said outer shell and spaced between the two groups ofperforations of one restriction and the two groups of perforations ofanother restriction, and an intermediate shell surrounding apertorateportion of said conduit separate from the groups of perforationsassociated with said restrictions.

15. A muiiler having an outer shell, inlet and discharge heads securedto said shell and provided with gas receiving and discharge openings, aperforate conduit connecting said openings and providing asubstantiallyv straight uninterrupted passage ior gases from saidreceiving opening to said discharge opening and provided at intervalsbetween perforations with restrictions serving to cause a portion of thegases in the conduit to pass outwardly through perforations into thespace between said conduit and said outer shell and back through otherperiorations into said conduit',

16. A muiiler having an outer shell, inlet and discharge heads securedto said shell and provided with gas receiving and discharge openings, aperforate conduit connecting said openings and providing a substantiallystraight uninterrupted passage for gases from said receiving opening tosaid discharge opening and provided at intervals between perforationswith restrictions serving to cause a portion of the gases in the conduitto pass outwardly through perforations into the space between saidconduit and said outer shell and back through other perforations intosaid conduit, and means in the space between said conduit and said outershell for determining the length of travel of sound waves in said spacebetween said conduit and outer shell to cause said sound waves whenreentering the conduit to be out of phase with sound waves passingstraight through said conduit.

GAILI C. STARKWEATHER. LUCIEN L. HAAS.

